Variable impedance device having movable core and mounting means



1964 w. A. MELANSON ETAL VARIABLE IMPEDANCE DEVICE HAVING MOVABLE CORE AND MOUNTING MEANS Filed Aug. 10, 1960 x l w J :1 H in 2 r f 0 WW a %M 2m 1 u .r z a w w W 0/0 V v 36 ifi H H 2 r \N, 1 m v w? 2 2 i w United States Patent 3,133,260 VARMBLE EMPEDANCE DEVICE HAVWG MOV- ABLE CORE AND MOUNTWG MEANS Wiiiiam A. ltdeianson, Lexington, Mesa, and Warren H.

West, Seabrooir Beach, N.H., assignors to Cambridge Thermionie Corporation, Cambridge, Mass, at corporation of Massachusetts Fiied Aug. i0, 196%, Ser. No. 43,604

It Ciaiins. ((Cl. Edd-"136) The field of this invention is that of variable impedance devices, more particularly of devices whose impedance can be varied by movement of a core element relative to a fixed element.

Objects of the invention are to provide a variable impedance device which can be finely and accurately adjusted, at a uniform rate not varied at random as a result of inherent construction and vibration or temperature changes to which the device may be subjected; to provide such a device having a wide range of adjustment for a given physical size, especially minimal length, and permitting adjustment either to increase or to decrease impedance with equal facility, accuracy and uniformity; to provide a device having the above properties, especially of exact and yet easy guidance of an adjustable core and of optimal dimensions, which can be simply and inexpensively manufactured and which can be conveniently mounted; and to provide such a device wherein the critical adjustment components are substantially protected from injury.

The substance of the invention can be briefly summarized as follows.

The variable impedance device according to the invention includes, in one principal aspect, an insulating tube having an impedance element mounted thereon, and a core adapted for axial movement within the tube for adjusting the impedance of the device. The core also has an axially-extending, threaded stem. Tube and core are supported on mounting means having a split, internallythreaded sleeve portion extending within the tube from one end axially to engage the threaded core stem, and having a flange portion holding an end of the tube on one side and carrying provisions extending oppositely of the sleeve for mounting the device. i

In another particularly valuable aspect, the core of this impedance device carries a resilient portion which slidably engages the tube for accurately centering the core.

'In a practical embodiment of the invention the mounting means has a split, internally-threaded sleeve portion which extends within the tube from one end for adjustably engaging the threaded core stem, having a flange portion abutting the tube end for locating the split sleeve within the tube, and the mounting means having an externally-threaded stud portion extending oppositely of the sleeve for mounting the device. The mounting means carries a cup-shaped connecting element having a base and a rim, the base being apertured and fitted over the stud portion of the mounting means and the rim being upon assembly swaged around the flange of the mounting means for gripping the tube end, thereby uniting mount i-ng means and tube. The resilient portion of the core is preferably a body of suitably resilient material, slightly 3,133,260 Patented May 12, 1964 oversized relative to the inner diameter of the insulating tube, such that it slidably and yieldably engages the tube for centering the core therein.

These and other objects and aspects of the invention will appear from the following detailed description of several practical embodiments thereof illustrating its novel characteristics.

The description refers to a drawing in which FIG. 1 is a section along the axis of a device according to the invention;

FIG. 2 is a front elevation of the device;

FIG. 3 is a section on lines '33 of H6. 1;

FIG. 4 is a partial section similar to FIG. 1, showing an alternative embodiment of the invention;

FIG. 5 is a partial section similar to FIG. 1 showing another alternative embodiment of the invention;

FIG. 6 is a partial section view similar to PEG. 1 showing a further alternative embodiment of the invention; and

FIGS. 7 and 8 are front views of washers adapted to be mounted on the core of the device.

Referring to FIGS. l3, numeral 11 indicates a tube of insulating material, preferably glass or ceramic material but also plastic compounds or any other insulating material which is relatively rigid. The tube 11 preferably has a bulge 12 at one end, and it has a smooth inner wall 14. An impedance element, such as the coil 17 with leads 18, can be mounted on the insulating tube in conventional manner. A metallic core 21, preferably molded from powdered or sintered magnetic metal, is disposed within the tube and adapted for axial movement therein by means of a threaded, axially extending stem 2-2 having flattened portions 24 or other tool engageable provisions such as a screw driver slot at the extending end. The core 21 carries a disc 26 of resilient material cemented thereto, the disc being somewhat over-sized relative to the insulating tube, just enough for yieldingly engaging the inner wall :14 of the tube to center the core therein, but permitting sliding movement of the core.

The disk 26 is preferably made of cementable Teflon, but it will be understood that plastics other than Teflon, such as synthetic rubber, can be used so long as they are sufliciently soft to deform for fitting the tube '11 and also withstand extremes of temperature, an operative range of from F. to +500 F. being sometimes required. The disks 26 can be of various shapes as will be described below, stamped or punched out from commercially available sheet material. They are cemented to the core for constructions as her example shown in FIG. 1, by means of a suitable adhesive such as epoxy resin. The adhesive is applied to both slug and disk, the parts are joined by means of an appropriate locating and centering fixture, and kept clamped together until the adhesive is set. in a practical embodiment, the diam eter of the Teflon washer is 0150:.001 inch and that of the core proper 0.145 inch, which dimensions are well suited to provide the above discussed characteristics of counteracting vibration and of exactly centering the core while permitting easy sliding and rotatory adjustment and avoiding unfavorable response to temperature changes to which metal components used for similar purposes are subjected. It will be evident that the material used for these washers must be compact and dimensionally stable in order to hold -the critical core gap to predetermined dimensions of the above indicated order of magnitude.

The mounting member 31 has a sleeve portion 32 which is axially split as at 33 to provide the resilient leaves 34 and which extends within the insulating tube 11. The sleeve is internally threaded, as at 35, for adjustably engaging the core stem 22. The mounting member 31 also has a flange portion or collar 36 adapted to abut the end bulge 12 of the insulating tube, and the roots of the leaves 34 between the slots 33 preferably reach to the inner face 36.1 of the flange. The mounting member 31 also has a stud portion 38, externally threaded as at 38.1, which extends oppositely of the sleeve portion 31. The stud portion 38 of the mounting member has an axial recess 38.2 which intercepts the threads 35 of the sleeve portion 32 and contains part of the core stem 22. Preferably the stud portion of the member 31 has a cordal flat 38.3 for a purpose to be described below. An annular spring 41, split as at 42, is fitted around the sleeve portion 32 adjacent its end, preferably being fitted within a groove 43 in the sleeve leaves 34, for clamping the sleeve inwardly to grip the core stem firmly and securely, in accordance with the principles set forth in Patent No. 2,899,220.

The cup-shaped connector element 51, having a base 52 and a rim 54, is provided with an aperture 56 corresponding in cross-section to the stud portion 38 of the member 31, and is fitted over the stud portion to engage the flange portion 36 of the member 31 within a second aperture 57. The rim 53 of the connector element 51 is swaged inwardly as at 58 to clamp the flange portion 36 of the member 31 and the bulge or lip 12 of the insulating tube 11 for uniting the connector, the mount, and tube. A rubber cushioning member 59 is preferably fitted between the flange portion 36 and the tube end 12 for preventing injury to the tube during swaging of the rim 53 of the connector element rim and for assuring firm, non-vibrating attachment of the three components.

If desired, the connector 51 can be provided with a hexagonal outer periphery readily engageable by a socket tool to facilitate mounting of the impedance device on an instrument panel.

In this embodiment, the core can be rotated and shifted by means of a tool inserted within the stud portion bore 38.2 to engage the flat portion 24 of the core stem for axially moving the core in either direction within the tube 11 to adjust the impedance value as defined by the coil 17 and the core 21. The adjusting tool must be inserted within the bore 38.2 and can be made to fill the bore, so that the tool cannot move transversely of the core stern axis during adjustment of the core. Therefore the core stem cannot be bent or twisted even though adjustment is carelessly made. Also, the finely machined core stem is by the walls of the bore 38.2 protected from blows or falls such as might occur during installation and use. The cordal segmental cut-out or flat 38.3 on the member 31 is adapted to engage a corresponding edge or edges of the connector aperture 56, for preventing rotation between these elements. If the device is mounted on an instrument panel by inserting the stud portion 38 into an aperture of the panel corresponding in shape to the connector aperture 56, a nut (not shown) can be fitted on the stud portion for securing the device to the panel. This permtis mounting of the impedance device with a single wrench or other turning tool.

The sleeve portion 32 which extends within the tube 11 is clamped adjacent its end by the spring 41 thus providing firm and secure support as close as possible to the core 21, whereby vibration of the core within the tube is substantially reduced. The disc 26 of plastic material, in engaging the tube provides further support for the core and centers the core within the tube, whereby random variation of impedance such as might be caused by vibrations, is substantially eliminated.

The two-part construction of the tube engaging means, with the mounting means 31 and the connector element 51 permits the convenient slotting of the sleeve 32 as at 33 to the full length of the sleeve. It will now be evident that, if the mounting means 31 and the connector 51 were formed in one piece, the tool most conveniently used for cutting the slots 33 would interfere with the rim 53 and a more careful and expensive manufacturing technique would be required.

This impedance device is assembled by inserting the mounting member 31 into the connector 51 such that the flange 36 rests on the bottom of the connector, the flattened thread portion 38.3 fitting the D-shaped aperture 56. The soft rubber washer 53 is then applied to the flange 36 whereupon the tube 11 is applied to the washer and the assembly completed by firmly rolling the rim 58 over the tube bulge 12. The tuning core 21 with its centering body 26 is then screwed into the torque sleeve component 32. It will be noted that the flat 38.3 on the threaded shank 38 secured the cup or connector 51 with its D-shaped aperture against rotation. This flat also prevents rotation of the assembly relatively to a panel or the like on which it is mounted if the latter has a D-hole similar to that of the connector 51. Upon such mounting on a panel or similar support, the latter is clamped between the flange 52 and a nut (not shown) on the mount stud 38. The core spindle 22 is protected within bore 38.2 and a tool therein inserted for engaging the square 24 is thus centered.

Alternative embodiments of the device provided by this invention are illustrated in FIGS. 4 to 7 wherein components similar in function to components shown in FIGS. 1 to 3 are identified by corresponding decimal numbers.

FIG. 4 shows a resilient washer 26.1 preferably made of Teflon or material offering similar advantages, and having an internally-threaded bore 26.11. The washer is thus engaged on the thread of the core stem adjacent the core and adapted slidingly and yieldingly to engage the insulating tube 11.1 for centering the core therein. Such a washer can be conveniently attached to the core and permits adjustment of the core in either direction with equal facility. The use for this washer of Teflon, which has low heat-expansion characteristics, assures that sliding engagement of the washer and the tube will not be varied during temperature changes to which the device might be subjected. The slug which is in this instance accessible at its free end, can be provided with a screw driver slot 21.15 in which case adjustment from either end becomes possible.

FIG. 5 shows a resilient washer 26.2 which has a threaded bore at 26.21 and is mounted on the core stem, and a nut 26.23 of approximately the same diameter as the core, is engaged on the core stem abutting the washer. This lock nut construction provides a convenient and especially secure attachment of the Washer and assures that it will remain in sliding engagement with the tube 11.2 over long periods of use. In this construction, if desired, the core may be slotted as at 21.25 for receiving a screw driver, whereby core adjustment can be accomplished from either end of the impedance device.

FIG. 6 shows a core unit 61 which is comprised of a core portion 62 made of powdered or sintered metal, and a washer portion 63 formed of Teflon material. Such a core unit can be conveniently formed by successively introducing the Teflon molding material and the powdered metal into a mold for pressing in otherwise conventional manner, whereby the powder pressed core and the Teflon portion become permanently joined by direct fusion. This core unit construction is inexpensive and assures that the core portion and washer portion are associated in proper coaxial relation, thereby assuring that the core will be accurately centered within the tube 11.2 without variation as the core is shifted and rotated in the tube.

FIG. 7 illustrates an alternative embodiment of the disk 26 incorporated in the device illustrated in FIGS. 1 to 3. In this construction the disk 26.5 is provided with at least three equally spaced notches 26.51, whereby the disk is adapted to engage the tube at equally spaced points indicated at 26.52. If desired, the washer 26.5 can have a threaded bore as at 26.53 for convenient attachment to the core stern. This construction assures proper centering of the core within the tube without requiring excessive forces for core adjustment.

FIG. 8 illustrates the possibility of using centering components of even more simple shape. The washer 26.6 of FIG. 8 has two flats 26.71, 26.72 and is intended for cementing to the end of a core according to FIG. 1. It will however be understood that it could be provided with a hole such as that of FIG. 7, and used in accordance with FIG. 5. Centering washers according to FIGS. 1 and 8 should be of cementable material, whereas this is not required for plates according to FIGS. 4, 5 and 7. The centering element according to FIG. 6 is formed directly in a die together with the core proper. The dimensions given above for a centering disk and a tube can serve as guides for the other embodiments, but it will be understood that the fit depends a good deal on material, dimensions, and use, so that some experimentation will be advisable in each case.

It will now be evident that impedance devices according to the invention offer the following advantages among others similarly appearing from the above description of several embodiments.

The length of the assembly is minimal because the torque device as well as the core are on one side of the mounting means, because the adjusting length of the core spindle lies within the torque device, and because the notching of the latter is independent of other portions of the device due to the two-piece construction separating tube and core supports.

The mounting stud of the core support has the triple function of mechanically protecting and electrically shielding the free end of the core spindle, of centering the adjusting tool, and of preventing rotation on the supporting panel.

The D-shaped core mount and connector have the double function of preventing rotation between these parts and between mount and panel.

The spring of the torque device which secures the core is protected within the tube for the impedance element.

The vibration length of the core spindle is especially short which essentially reduces vibration even without anti-vibration and centering disk.

The centering body, disk or washer, of thermally insensitive material at the end of the core promotes easy sliding of the core within the tube in either direction, counteracts excessive expansion upon temperature changes as compared to metal structures for similar purposes, avoids tuning irregularities introduced by the electric effects of metal structures, and permits especially simple and inexpensive assembly techniques.

The yielding centering body which snugly contacts the tube is a very eiiectively dampening means; together with the short vibration length of the core spindle this practically eliminates vibration effects which very adversely affect constancy of impedance.

The grounding region of the core being within or very close to the ground plane of the mounting support such as a chassis, better grounding is achieved, and the possibility of spurious chassis currents is minimized.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. A variable impedance device comprising: an insulating tubular support for an impedance element; a core mounted for axial movement within said tubular support to adjust the impedance, said core having an axially-exsaid tubular support to said mounting means at said flange portion.

2. Device according to claim 1 further comprising a resilient body of dimensionally stable material on said core for slidably engaging said tubular support for centering the core therein and for attenuating vibration of the core.

3. Device according to claim 2 wherein said body is cemented to the outer end of said core opposite to said stem.

4. Device according to claim 2 wherein said body is arranged at the inner end of said core and has a threaded aperture fitting the thread of said stem.

5. Device according to claim 2 wherein said body is arranged at the inner end of said core and has a smooth aperture fitting said stem, and further comprising a nut fitting the thread of said stem for pressing the body against the core.

6. Device according to claim 2 wherein said core is made of pressurably molded metal, said body is made of plastic material, and said body is directly fused to said core.

7. Device according to claim 2, wherein said body comprises a disk of resilient material having a plurality of equally spaced peripheral notches for partially relieving engagement with said tube.

8. A variable impedance device comprising: an insulating tubular support for an impedance element; a core mounted for axial movement within said tubular support to adjust the impedance, said core having an axially-extending, threaded stem and a resilient portion of dimensionally stable material mounted on the core slidably engaging said tubular support for centering the core therein and for attenuating mechanical vibration; mounting means having a split, resiliently compressed and internally-threaded sleeve portion extending within the tubular support for adjustably engaging said threaded core stem, said mounting means having a flange portion bearing against said tubular support, and said mounting means having a mounting stud portion extending oppositely of said sleeve portion; and means for connecting said tubulm support to said mounting means at said flange portion.

9. A variable impedance device comprising: an insulating tubular support for an impedance element; a core mounted for axial movement within said tubular support to adjust the impedance, said core having an axially-extending, threaded stem; mounting means having a flange portion having a face bearing against said tubular support, a longitudinally split, internally-threaded sleeve portion extending from said face of the flange portion within the tubular support and carrying a compression spring means on its end for frictionally engaging said threaded core stem, and said mounting means having a mounting stud portion extending oppositely of said sleeve portion and having an axial bore for receiving said core stem and extending from said sleeve portion; and means for connecting said tubular support to said mounting means at said flange portion.

10. A variable impedance device comprising: an insulating tubular support for an impedance element; a core mounted for axial movement within said tubular support to adjust the impedance, said core having an axially-extending, threaded stem; a resilient body of dimensionally stable material mounted on said core for slidably engaging said tubular support for centering the core therein and for attenuating vibration of the core; mounting means having a longitudinally split, resiliently compressed and internally-threaded sleeve portion extending Within the tubular support for adjustably engaging said threaded core stem, said mounting means having a collar bearing against said tubular support where said sleeve portion extends from said collar toward said core, and said mounting means having a mounting stud portion extending from said collar oppositely of said sleeve portion and having an axial bore for receiving said core stem and extending from said sleeve portion; and for connecting said tubular support and said mounting means at said collar.

References Cited in the file of this patent UNITED STATES PATENTS 2,236,292 Kirk Mar. 25, 1941 2,318,415 Patzschke et a1 May 4, 1943 2,899,220 Abrams Aug. 11, 1959 FOREIGN PATENTS 827,041 France Jan. 18, 1938 

1. A VARIABLE IMPEDANCE DEVICE COMPRISING: AN INSULATING TUBULAR SUPPORT FOR AN IMPEDANCE ELEMENT; A CORE MOUNTED FOR AXIAL MOVEMENT WITHIN SAID TUBULAR SUPPORT TO ADJUST THE IMPEDANCE, SAID CORE HAVING AN AXIALLY-EXTENDING, THREADED STEM; MOUNTING MEANS HAVING A LONGITUDINALLY SPLIT, RESILIENTLY COMPRESSED AND INTERNALLYTHREADED SLEEVE PORTION EXTENDING WITHIN THE TUBULAR SUPPORT FOR ADJUSTABLY ENGAGING SAID THREADED CORE STEM, SAID MOUNTING MEANS HAVING A FLANGE PORTION BEARING AGAINST SAID TUBULAR SUPPORT WHERE SAID SLEEVE PORTION EXTENDS FROM SAID FLANGE PORTION TOWARD SAID CORE, AND SAID MOUNTING MEANS HAVING A MOUNTING STUD PORTION EXTENDING OPPOSITELY OF SAID SLEEVE PORTION; AND MEANS FOR CONNECTING SAID TUBULAR SUPPORT TO SAID MOUNTING MEANS AT SAID FLANGE PORTION. 